Modern air conditioning compressors are controlled in a variety of ways to deliver the desired amount of refrigerant to the evaporator. One way of controlling this amount of refrigerant is by controlling the drawing or suction pressure of the refrigerant by the compressor from the evaporator. The drawing pressure is measured in the suction line between the evaporator and the compressor, while the suction pressure control is carried out by determining the temperature of the evaporator surface in order to alter the suction pressure. When a vehicle occupant desires cooler air to be blown into the vehicle compartment, the occupant turns the blower, or fan speed, to high. This increases the air passing through the evaporator and raises the temperature of the evaporator surface, which causes the compressor to draw coolant through the evaporator for a longer period of time in order to compress enough coolant for enough time in order to meet the desired cooling level of the occupant. Likewise, when the occupant desires the blowing air to be at a temperature higher than the current blowing air temperature, the occupant reduces the fan speed or blower speed. This causes the evaporator surface temperature to become colder, which in turn signals the compressor to reduce the suction pressure and time that the compressor compresses during a given cycle. This type of system has a drawback in that it does not know how much torque the compressor absorbs from the engine. A further limitation of this system is its inability to optimize fuel economy because the compressor is always maximizing its displacement which also maximizes its horsepower draw from the engine, which supplies rotational power to the air conditioning compressor. This system fails to optimize horsepower draw from the engine, which is a minimization of that horsepower draw from the engine.
Another current air conditioning control system is a torque-controlled system that manages the engine torque consumed by the compressor. That is, within the structure of the compressor, there is a small orifice measurement device. Because of this small orifice, it is possible to obtain the pressure differential in the coolant line before and after the stroke of the compressor. Because the compressor is a variable displacement compressor, it is possible to obtain a mass flow rate differential and pressure differential of the coolant across the orifice and therefore, adjust the displacement or stroke of the compressor output accordingly.
Both of the above control methods are passive control methods. That is, neither of the above control methods measures quantities of temperature or humidity of the air passing into the evaporator. Because of this, neither system is capable of determining what mass flow rate at which to start the compressor upon start-up of the compressor when the air conditioning system is activated. After the air conditioning system is operating, the control system will know the temperature of the air coming out of the evaporator and then further adjustments can be made. Operation of the compressor during this pre-adjustment period is inefficient and consumes horsepower from the engine, thus limiting the maximum fuel economy possible.
What is needed then is a device that does not suffer from the above limitations. This in turn, will provide a device that measures the temperature and humidity of the air entering the evaporator and the temperature set within an interior of an automobile in order to initially set and subsequently adjust a compressor stroke upon start-up of the air conditioning system.